Abstract

Background

Cancer chemoprevention is a new approach in cancer prevention, in which chemical agents
are used to prevent cancer in normal and/or high-risk populations. Although chemoprevention
has shown promise in some epithelial cancers, currently available preventive agents
are limited and the agents are costly, generally with side effects. Natural products,
such as grape seed, green tea, and certain herbs have demonstrated anti-cancer effects.
To find a natural product that can be used in chemoprevention of cancer, we tested
Arizona cactus fruit solution, the aqueous extracts of cactus pear, for its anti-cancer
effects in cultured cells and in an animal model.

Method

Aqueous extracts of cactus pear were used to treat immortalized ovarian and cervical
epithelial cells, as well as ovarian, cervical, and bladder cancer cells. Aqueous
extracts of cactus pear were used at six concentrations (0, 0.5, 1, 5, 10 or 25%)
to treat cells for 1, 3, or 5 days. Growth inhibition, apoptosis induction, and cell
cycle changes were analyzed in the cultured cells; the suppression of tumor growth
in nude mice was evaluated and compared with the effect of a synthetic retinoid N-(4-hydroxyphernyl)
retinamide (4-HPR), which is currently used as a chemoprevention agent. Immunohistochemistry
staining of tissue samples from animal tumors was performed to examine the gene expression.

Results

Cells exposed to cactus pear extracts had a significant increase in apoptosis and
growth inhibition in both immortalized epithelial cells and cancer cells in a dose-
and time-dependent manner. It also affected cell cycle of cancer cells by increasing
G1 and decreasing G2 and S phases. Both 4-HPR and cactus pear extracts significantly
suppressed tumor growth in nude mice, increased annexin IV expression, and decreased
VEGF expression.

Conclusion

Arizona cactus pear extracts effectively inhibited cell growth in several different
immortalized and cancer cell cultures, suppressed tumor growth in nude mice, and modulated
expression of tumor-related genes. These effects were comparable with those caused
by a synthetic retinoid currently used in chemoprevention trials. The mechanism of
the anti-cancer effects of cactus pear extracts needs to be further studied.